This invention relates to electrical connectors. More particularly this invention relates to zero insertion force electrical connectors. Most particularly this invention relates to a low cost, high density connector to interconnect primarily conductive ink circuits (CIC), flexible printed circuits (FPC), and/or flat flexible cables (FFC), with out the presence of at least one additional stiffener, as required with conventional zero insertion force connectors.
In today""s electronics market, manufacturers are placing emphasis on increasing their product""s reliability and reducing assembly costs to remain competitive. A primary focus of each manufacturer is to reduce the cost and increase the circuit density associated with interconnecting the sub-assemblies and components found within its products. Another emerging focus in today""s electronics market is to pack more electronic functions into smaller packages. This means higher density (for example 0.0125 inches on center) modules, each requiring multiple high density interconnections to other modules.
In electrical systems, flexible printed circuits are employed as electrical jumpers or cables for interconnecting rows of terminal pins or pads of printed circuit boards. Such flexible printed circuits are generally connected to a printed circuit board using a connector. Conventional connector manufacturers compete with each other using the same basic technology, individual stamped contacts molded into a plastic housing. This structure is then soldered to a printed circuit board (PCB) and is then ready to receive a flexible jumper or interconnect circuit. Many of these conventional connectors are of the zero insertion force (ZIF) variety, which require the application of minimal forces during the process of inserting the flexible circuit into the connector. These ZIF connectors thus reduce the likelihood of circuit damage during the connection process.
All of today""s ZIF connectors use either the edge of the interconnect circuit or a precisely located hole to accurately align the conductors of the flexible circuit to the connector""s contacts. This requires circuit manufacturers to precisely control both the thickness and width of a flexible circuit""s terminating ends. If a circuit is too thin, the contacts will not attain the required deflection needed to achieve and maintain the desired contact force. Generally, tolerances must be maintained within 0.003 inches. To accurately outline a circuit and control the required tolerances requires an expensive precise outline die.
Another obstacle encountered in conventional circuit connector technology centers around a tendency of flexible circuits to shrink somewhat after their manufacture. When working with larger flexible circuits, the shrinkage problem can be significant enough to result in significant alignment problems. As such, outline dies are usually constrained to outline a 6 inch by 6 inch area. This size restriction adds labor costs and reduces yield.
In addition to size restrictions, flexible circuits also require the precise attachment of a support stiffener. This stiffener is required to lift the flexible circuits into connection with a conventional connector""s contacts and add the structural support necessary to ensure the thin flexible circuit enters into the connector""s opening. The precise outlining and stiffener attachment process is cumbersome and costly, and frequently the cause of poor yields and system failures.
In addition, existing ZIF connectors incorporate a high pressure wiping contact system. This approach, although effective on copper circuits, destroys conductive ink circuits (CIC).
Existing ZIF connectors also do not adequately restrain the flexible circuit and are notorious for having circuits pop out during assembly and even during use. The inability of current systems to adequately restrain the circuit leads to the potential of causing a catastrophic system failure. To add to the instability problem, existing connectors offer a one point contact system. Having only one point of contact has been a source of numerous failures attributed to contact falling over plating voids, a spot of adhesive or other foreign material on the conductor of the flexible circuit.
Thus, there is a need for a low cost, high density, circuit to printed circuit board stored energy connector that can interconnect the delicate contacts of conductive ink circuits, flexible printed circuits, and/or flat flexible cables to printed circuit boards.
A circuit to printed circuit board stored energy connector is disclosed which is intended to be a low cost, high density connector. Also disclosed is a method of interconnection using the connector of the present invention. The connector is designed to precisely align and interconnect conductors of conductive ink circuits (CIC), flexible printed circuits (FPC), round wire interconnects (RWI) and/or flat flexible cables (FFC), (collectively referred to hereinafter as xe2x80x9cflexible circuitsxe2x80x9d) to a conductive spring in the connector. The spring is then connected to mating contacts on printed circuit boards (PCB""s). The disclosed connector relies in part upon the flexible circuit conductors themselves for alignment purposes and thus eliminates the need for precise control of the outside dimensions of a flexible circuit""s dielectric backplane or a precisely located alignment hole in the flexible circuit. The connector is of the zero insertion force (ZIF) variety and is a high density surface mount connector capable of terminating conductors on 0.006 inch pitch centers.
The disclosed circuit to printed circuit board stored energy connector comprises the following major components: an actuator that cooperates with a component retaining shell, and at least one spring contact housed in a spring support module.
The connector uses the flexible circuit""s existing features (its outline and conductors) to initially accurately align the conductors of the flexible circuit to their mating spring contacts in the connector. Unlike previous systems, the invention uses a xe2x80x9cbuilt-inxe2x80x9d circuit to contact alignment mechanism. The mechanism includes circuit locating arms, a circuit compression flap, and conductor alignment notches. For initial general alignment, the flexible circuit is slid into a circuit alignment cavity which allows the tapered alignment notches to accurately locate the leading edge of the flexible circuit. The flexible circuit is held in place by a circuit retaining button designed to deflect the flexible circuit into a receptacle found in the component retaining shell.
In order to further align the flexible circuit in the connector, circuit locating arms, positioned on each side of the flexible circuit aid in locating the conductors of the flexible circuit over the tapered alignment notches. Finally, as an actuator is closed over the flexible circuit, the compression flap forces the conductors of the flexible circuit into the tapered alignment notches, completing the alignment process. Circuit to circuit (flexible circuit to printed circuit board) interconnection is then achieved as the actuator applies the force necessary to provide the desired contact pressure between the subject circuit and the spring contact. A micro-wiping action occurs as the spring contact slides across the back of the dielectric of the flexible circuit while applying an ever increasing force to each contact of the flexible circuit until the desired interconnection results are achieved. To further insure a stable contact, the invention provides a redundant two point contact.
Thus an aspect of the invention is to provide a low cost, high density connector usable with conductive ink circuits, flexible printed circuits, and/or flat flexible cable.
Another aspect of the invention is to provide a connector that does not require the attachment of any added stiffeners in order to align a subject circuit to its contacts.
A further aspect of the invention is that the invention does not require that the thickness of the subject circuit be tightly controlled. The invention can accommodate varying thicknesses.
A still further aspect of the invention is that the invention eliminates the need for strain relief/alignment holes to be installed in the subject circuit by using the subject circuit itself to aid in alignment.
Yet another aspect of the invention is that the invention eliminates the conventional high pressure wiping contact of prior connectors, thus allowing the invention to be used with subject circuits that are typically damaged or destroyed by conventional connectors.
Another aspect of the invention provides a two point locking system to lock the subject circuit in place in the connector.
In addition, another aspect of the invention provides redundant two points of contact between the subject circuit and the printed circuit board which enhances reliability.
A further aspect of the invention provides accommodation of varying thickness of the subject circuit, in that the spring contact is self-setting and adjusts to the thickness of the particular circuit inserted into the connector, and provides a less severe wiping contact upon activation of the actuator and spring contact. The spring contact can, however, also be shaped to provide a traditional wiping contact for use with metal based circuits.
A further aspect of the invention is that, because the spring contact is flat and self-setting it is much less expensive and complex to manufacture.
These and further aspects and embodiments of the invention will become readily apparent from the following exemplary detailed description and appended claims.